1. Field of the Invention
The present invention relates to a photocatalytic fiber favorable for forming sanitary materials such as mask, medical cloth, bandage, and gauze, room decorative articles such as curtain, carpet and wall paper, clothing items such as uniform and clothes, livingwares such as towel, sheets and beddings and various filters which excel in decomposition ability of harmful components such as harmful materials or disease agents contained in air, soil and water, a fabric with excellent photocatalytic function using the fiber, and a fabric product using the fabric which is capable of exhibiting excellent photocatalytic function for prolonged period.
2. Description of the Related Art
The sick house syndrome caused by harmful materials such as formaldehyde which are produced from building materials or adhesive bonds used for wall papers in the house has become an issue. As means to remove such harmful materials, for example, a method, in which activated carbon or chemical absorbent is contained in the building materials or wall papers, has been proposed.
It may be possible for the activated carbon or chemical absorbent to absorb harmful materials such as formaldehyde to some extent, however, there is a problem such that the absorption ability relative to the harmful materials gradually fade off and/or disappear after long-term use.
On the other hand, mask use has been drawing an attention as an effective means for protecting against infectious diseases such as cold, influenza, SARS, etc. or measures against allergies to pollen, house dust, etc. The mask has a filter function similar to those of gauze or nonwoven cloth and prevents virus or pollen from invading inside the body by its absorption ability and further parallel use of activated carbon fiber.
It is possible to physically catch disease agents such as bacteria, virus, pollen, etc. in this case, however, it is impossible to kill or inactivate these disease agents and it is difficult to take preventive measures against infectious diseases to perfection.
In recent years, photocatalytic activity (herein after, may be referred to as “photocatalytic function”), which exhibits oxidative decomposition effect, antibacterial effect, antifouling effect, etc., of certain semiconductor materials, e.g. titanium dioxide (TiO2), has been receiving attention to settle above issues. In general, when the semiconductor materials having photocatalytic activity absorb light with an energy corresponding to the band gap between the valence band and the conductor band, the electron present in the valence band transits to the conductor band. The electron which transited to the conductor band have characteristics of moving to substances adsorbed on the surface of the semiconductor material having the photocatalytic activity and, when substances are adsorbed on the surface of the semiconductor material, the substances are reduced by the electron. Due to the transition, a hole is generated in the valence band. The hole generated in the valence band have characteristics of stripping the electron from the substance adsorbed on the surface of the semiconductor material having the photocatalytic activity and, when substances are adsorbed on the surface of the semiconductor material, the substances are oxidized as a result of the strip of the electron thereof by the hole. To explain the above-mentioned phenomenon more specifically, taking titanium dioxide having particularly excellent photocatalytic activity as an example, when titanium dioxide absorbs light with energy equivalent to band gap between the valence band and conduction band, an electron in the valence band of the titanium dioxide transits to the conduction band and the transited electron reduces oxygen in the air, thereby allowing generation of superoxide anion (.O2−). In contrast, as a result of the transition of the electron, a hole is generated in the valence band and the generated hole allows the generation of hydroxy radical (.OH) by oxygenating water adsorbed on the surface of the titanium dioxide. The resulting hydroxy radical is strongly oxidative, and thus when organic substances or the like are adsorbed on the surface of the titanium dioxide, the organic substances or the like are decomposed by the action of the hydroxy radical and finally decomposed to water and carbon dioxide. In this way, when the semiconductor materials having photocatalytic activity, such as titanium dioxide, are exposed to light with an energy equivalent to band gap between the valence band and conduction band of the semiconductor materials, the semiconductor materials absorb the light and organic substances or the like absorbed on the surface are decomposed. Thus, oxidative decomposition effect, antibacterial effect, antifouling effect, etc. are achieved.
Since the titanium dioxide has low absorption ability toward materials, it is often used simultaneously with the absorbent such as activated carbon, and oxidative decomposition effect, antibacterial effect, antifouling effect, etc. are exhibited by decomposing the material absorbed by the absorbent with the titanium dioxide. The titanium dioxide and absorbent are attached to the target (base material) such as mask, etc. by using binders or adhesives.
However, the viruses smaller than the absorbent particle hardly comes in contact with the titanium oxide when they are absorbed by the absorbent, thereby making it difficult to decompose and remove all the material absorbed by the absorbent. Moreover, because the titanium dioxide decomposes organic materials as described above, organic materials are not usable as binders or adhesives and particular kind of binders or adhesives such as inorganic binders must be used. If organic binders, etc. are used, the surface of photocatalyst must be coated with silica in order to avoid direct contact with binders or adhesives. Furthermore, when binders or adhesives are used, photocatalyst is buried inside of these binders or adhesives and the buried portion does not exhibit photocatalytic function, thereby degrading the photocatalytic function and possibly making it uneconomical because of the wasted use of expensive photocatalyst. And also, binders or adhesives may impair the texture of the mask.
Further, a method in which a photocatalyst is contained in the base material by dipping the base material such as mask in a photocatalytic solution without a use of binders, etc. and a method in which photocatalytic solution is sprayed to the base material for adhesion have been performed.
In these cases, however, binding property between the surface of the base material and titanium dioxide is insufficient, and most of the titanium dioxide falls off from the base material by washing, etc., significantly degrading the photocatalytic function. And fibers of the mask, etc. are decomposed by the photocatalytic reaction of the titanium dioxide, degrading the strength.
At the same time, a photocatalytic apatite which has both of photocatalytic function and absorption ability toward materials has been developed as a photocatalyst. It is unnecessary for the photocatalytic apatite to use absorbent simultaneously as for the titanium dioxide because of its excellent absorption property. Moreover, since decomposition of fiber does not occur, any binders or adhesives can be used and there is no need for the surface to be coated with silica.
The methods for attaching the photocatalytic apatite to the base material such as a method in which a base material such as mask is dipped in a photocatalytic solution as similar to the titanium dioxide (Japanese Patent Application Laid-Open (JP-A) No. 2005-177320) and a method in which the photocatalytic apatite is attached to the base material by using binders or adhesives (JP-A No. 2005-124777) have been disclosed. In the invention disclosed in JP-A No. 2005-124777, a method for preventing dropout of the photocatalytic apatite from the base material by disposing a protective layer on the surface of the base material to which the photocatalytic apatite is attached is further disclosed.
In this case, however, when binders or adhesives are used for adhesion to the base material, photocatalytic apatite is buried in these binders or adhesives, resulting in degraded photocatalytic function and making it uneconomical. And also, when binders, etc. are used, or when the photocatalytic apatite is attached by dipping, the photocatalytic apatite is attached only to the surface of the base material, and a problem still remains such that the photocatalytic apatite is likely to fall off by washing.
Therefore, an appropriate proposal of the product such as mask which excels in durability without impairment of the strength or texture of the base material, excels in decomposition ability against the harmful components such as harmful materials or disease agents contained in air, soil and water, is capable of exhibiting excellent photocatalytic function for prolonged period and can be mass-produced at low cost, has not been provided in the existing situation.
The present invention is intended to settle above existing issues and achieve the following purposes.
The purpose of the present invention is to provide a photocatalytic fiber which excels in durability, and decomposition ability against the harmful components such as harmful materials or disease agents contained in air, soil and water, can be mass-produced at low cost, and is favorable for forming sanitary materials such as mask, medical cloth, bandage, and gauze, room decorative articles such as curtain, carpet and wall paper, clothing items such as uniform and clothes, livingwares such as towel, sheets and beddings and various filters. Also provided is a fabric which excels in photocatalytic function and durability, can be mass-produced at low cost and is favorable for forming sanitary materials such as mask, medical cloth, bandage, and gauze, room decorative articles such as curtain, carpet and wall paper, clothing items such as uniform and clothes, livingwares such as towel, sheets and beddings and various filters by using the fiber. And also provided is a fabric product including sanitary materials such as mask, medical cloth, bandage, and gauze, room decorative articles such as curtain, carpet and wall paper, clothing items such as uniform and clothes, livingwares such as towel, sheets and beddings and various filters which can exhibit excellent photocatalytic function for prolonged period.
As a result of dedicated investigation conducted on the issues, the present inventors have obtained the following knowledge. It has been found that by using the photocatalytic apatite as a photocatalyst, an excellent photocatalytic function can be obtained without degrading the fiber even if it is directly attached to the fiber. Moreover, it has been found that by attaching the photocatalyst to the fiber forming the fabric for forming a mask, etc. and forming the fabric with the fiber, instead of attaching the photocatalyst on the surface of the base material, a solid binding property between the fabric and the photocatalyst can be obtained without a use of binders, etc. because the photocatalyst can be physically fixed in meshes or crossings of the fiber.